Without doubt, the longest faces can currently be found in the McLaren garage. The team's renowned resilience and resourcefulness look like being tested to the full.

Publicly, team officials dismiss the idea that the next two races in Belgium on Sunday and Italy in two weeks' time will make or break their title challenge this season.

Privately, however, there is reluctant acknowledgement that they have to score heavily at these final two European low downforce tracks where straight-line speed - where McLaren are stronger than their title rivals - can be decisive.

In order to see this content you need to have both Javascript enabled and Flash installed. Visit BBC Webwise for full instructions. If you're reading via RSS, you'll need to visit the blog to access this content.

As one team member put it succinctly: "It'll be all over for us if we don't. Red Bull will walk it in Singapore (first of the final five long-haul races), and be strong elsewhere."

While Sebastian Vettel happily described himself as "carefully optimistic" about Red Bull's prospects for the weekend, the normally upbeat Lewis Hamilton has been unnaturally pessimistic, seemingly resigned to chasing Red Bull's shadows for the remainder of the year.

"I don't think anything's going to change here. The car's still not quick enough compared to the others.

"We have to understand where the extra time and downforce is - and only once we've done that can we really move forward," he said on Thursday.

Now, I understand the McLaren engineers believe that a clever trade-off between more downforce and less drag thanks to their efficient F-duct aerodynamic device should make a difference here.

Yes, the Red Bulls will be quick through the long corners in Spa's middle sector, but McLaren should have the stronger performance along the straights in the first and final sectors to offset Red Bull's greater grip.

Not enough, probably, to find the margin of 1.7 seconds that Red Bull enjoyed over McLaren in Hungary but sufficient to be significant podium contenders.

Nonetheless, such a downbeat assessment of his car's current competitiveness is a vivid contrast to the optimism within McLaren at Silverstone last month.

Unfortunately the gains have not come close to fulfilling McLaren predictions. If anything, Button and Hamilton have found the car's balance worse.

Red Bull have continued to improve their performance since the British Grand Prix - as have Ferrari, whose own version of the blown diffuser has worked without problems since it was introduced in Valencia, the race before Silverstone.

Now, we've seen this before when Mark Webber and Red Bull hit the front after Monaco. It appeared that the team were all set to capitalise on their advantage and take charge of the title race.

On that occasion McLaren struck back.

But this time they feel more vulnerable to attack, and their frustration is fuelled by the continuing controversy over flexible bodywork.

In order to see this content you need to have both Javascript enabled and Flash installed. Visit BBC Webwise for full instructions. If you're reading via RSS, you'll need to visit the blog to access this content.

They believe that Red Bull and Ferrari have made their performance leaps because their front wings and the front part of the car's floor - frequently referred to as the 'bib' - are flexing excessively outside the regulation limits.

If you watched the last two races, you would have seen slow-motion footage of the front wings of the Red Bull, Ferrari and McLaren while the cars were on the track.

While McLaren's is very stiff and well clear of the road, the wings on the Red Bull and Ferrari appear to be almost touching it.

The team believe that the new FIA load tests, particularly on the rigidity of the floor at the Italian Grand Prix, will have an impact on their rivals' level of performance.

In the words of Jenson Button on Thursday: "I'd be amazed if there wasn't a difference (at Monza)."

One engineer I spoke to claims that Red Bull and Ferrari have a series of sections in their floor which allows the 'bib' to move, creating greater downforce behind the front wing.

The regulations state that the floor must be one solid piece.

Another engineer told me that if the other two teams have been doing this and are forced to make changes, then McLaren could find an extra 0.7secs, bringing them back into much stronger contention.

Not just at Monza, but for the championship run-in.

But he also stressed that the team has to be prepared for Red Bull and Ferrari to pass the new tests, in which case McLaren will be left to rely on their own technical talents to make up lost ground.

It should be emphasised that each time this season Red Bull have come under scrutiny for alleged technical irregularities, the FIA has consistently found no fault.

"We are confident that we will comply with whatever tests there are," said team principal Christian Horner.

"The new test will affect us only as much as any other team. If people are complaining, it shows that they don't know what we're up to.

Remember also that where once McLaren's championship ambitions looked to be a straight fight against Red Bull, now Ferrari's Fernando Alonso is back in the thick of it, only 20 points off leader Webber.

Ferrari, I understand, have reworked the rear of their car - with a new blown diffuser in which the exhaust gases blow through as well as over the new floor for the first time, as well as modified rear suspension and a new gearbox casing.

Their concern is over engines. Both Alonso and Felipe Massa have already used six of their season's allocation of eight.

If they follow the lead of some teams planning to use new units at both the power tracks of Spa and Monza, that could become a big issue for Alonso over the final five races.

For this weekend, though, Hamilton and Button, F1's two most recent champions - both of them wet-weather specialists - have to hope that McLaren can maximise what they have, otherwise they will feel like they're pushing water up Eau Rouge until November.